Canada has been missing 40% of severe pregnancy complications by only watching the delivery room

When Canadian hospitals count severe maternal complications, they count what happens during labor and delivery. That's it. The monitoring window opens when contractions start and closes when the patient is discharged from the obstetric unit.

A study of nearly 1.1 million births in Ontario has found that this window misses more than 40% of cases.

The surveillance blind spots

Severe maternal morbidity (SMM) encompasses pregnancy complications that can result in death, extended hospitalization, or long-term disability - events like severe hemorrhage, preeclampsia, sepsis, and organ failure. In Canada, these events are tracked during the labor and delivery period. But the human body doesn't confine its complications to a convenient clinical window.

The study, published in the Canadian Medical Association Journal, extended the surveillance period from conception through six weeks postpartum. Researchers from McMaster University, Hamilton Health Sciences, and St. Joseph's Healthcare Hamilton analyzed all births from 20 weeks' gestation in Ontario between April 2012 and March 2021, using linked administrative and clinical data from ICES.

The overall rate of SMM was 27.24 per 1,000 births - translating to roughly 10,000 people per year in Canada experiencing severe pregnancy-related complications. Of those events, 16% occurred during the prenatal period, 55% during labor and delivery, and 29% in the six weeks after birth.

The labor-and-delivery-only approach captures barely half the picture.

Where complications actually happen

The types of complications shifted across periods. Severe hemorrhage, severe preeclampsia, and sepsis were the most common overall. But acute appendicitis dominated the prenatal period, and sepsis was the leading event postpartum.

Notably, 19% of all people who experienced a severe event visited an emergency department - mostly during the prenatal and postnatal periods, not during labor. These are patients showing up at the ER with pregnancy-related emergencies that the maternity care system has already discharged or not yet admitted.

This finding aligns with coroner's data from Ontario showing that most maternal deaths occur outside the labor and delivery window: 47% prenatally and 46% postpartum. The events that kill pregnant and recently pregnant people are happening precisely during the periods that current surveillance doesn't cover.

Risk factors change with timing

The study found that risk factors for severe complications vary depending on when the event occurs. Complication rates during labor and delivery and in the postpartum period were highest among the youngest and oldest parents. But prenatal complications were disproportionately concentrated among those aged 15-24.

Common risk factors across all periods included first pregnancy, maternal race, pre-existing medical conditions, multiple-fetus pregnancies, immigrant status, low income, rural or remote residence, substance use during pregnancy, and exposure to assault. Type 1 diabetes had the strongest association with prenatal severe events.

These patterns suggest that different time windows require different screening and prevention strategies - a one-size-fits-all approach to risk assessment will miss vulnerabilities that emerge or shift across the pregnancy timeline.

A system designed around the delivery room

Senior author Giulia Muraca, a perinatal epidemiologist at McMaster University, framed the problem as structural. Severe maternal complications are not just a delivery room issue, she said - they occur across pregnancy and after birth, and many first appear in emergency departments rather than obstetric units. Improving maternal safety requires a whole-system approach involving emergency care, primary care, maternity teams, and postpartum follow-up.

The authors also noted that suboptimal access to primary care and declining availability of ambulatory obstetrical care in the postpartum period in Ontario leave many people without adequate care after childbirth - precisely when 29% of severe events are occurring.

Aligning with WHO guidance

Extending surveillance from conception to six weeks postpartum would align Canadian practice with World Health Organization guidance. The WHO has long recommended this broader window for monitoring maternal outcomes, recognizing that the risks of pregnancy extend well beyond the delivery itself.

The practical implications are concrete: postpartum home monitoring of vital signs like heart rate and blood pressure for individuals at increased risk could catch developing sepsis or preeclampsia before they become emergencies. Prenatal screening for conditions like appendicitis and Type 1 diabetes complications could identify high-risk patients earlier. And emergency departments need protocols that recognize pregnancy-related presentations even in patients who are no longer obviously pregnant.

This is a single-province observational study using administrative data, with all the limitations that entails - coding errors, missing variables, and inability to establish causation. But with a sample of 1.1 million births and a finding that the current surveillance system misses four out of every ten severe events, the direction of the evidence is clear. Watching only the delivery room is not enough.